docs: def serialize(self):
          """
          Convert an association to KV form.
  
          @return: String in KV form suitable for deserialization by
              deserialize.
  
          @rtype: str
          """
          data = {
              'version':'2',
              'handle':self.handle,
              'secret':oidutil.toBase64(self.secret),
              'issued':str(int(self.issued)),
              'lifetime':str(int(self.lifetime)),
              'assoc_type':self.assoc_type
              }
  
          assert len(data) == len(self.assoc_keys)
          pairs = []
          for field_name in self.assoc_keys:
              pairs.append((field_name, data[field_name]))
  
          return kvform.seqToKV(pairs, strict=True)